Rotary shaft seal

Abstract

The present invention is directed to a rotary shaft seal assembly and, more particularly, to an assembly including a continuous, annular, but axially variable seal for providing hydrodynamic lubrication between the seal and rotating shaft. The seal assembly uses differential pressures to maintain the seal compressed as it wears. The present system is particularly useful in drilling motors utilizing the movement of drilling fluid under pressure to operate the motor parts and thereby to drive a drill bit. The abrasive drilling fluid environment in a borehole is detrimental to the moving parts in such a system, and especially destructive to the bearings and seals. The present system utilizes a sealing member arranged in a continuous, annular, but axially variable path between the rotating shaft and housing of such a motor. Annular seal mounting members are positioned above and below the seal and have surfaces to matingly engage the seal member. The mounting elements are arranged to move relative to one another. A pressure differential developed across the motor is communicated to the respective mounting elements to urge the elements toward one another and thereby compress the seal member therebetween to accommodate wear take-up on the seal member. An oil chamber above the upper mounting element communicates drilling fluid pressure inside the drill pipe to the upper mounting element. The pressure of the annular space below the motor housing is communicated to the lower mounting element by means of a lower chamber.

What is claimed is: 
     
       1. A rotary shaft seal system for sealing an annular space between a rotating shaft and its housing, comprising: annular seal means having upper and lower engaging surfaces and having an axially variable configuration about a rotating shaft so that one sealing surface of said seal means slidably engages said rotating shaft;   first and second means for matingly engaging the upper and lower engaging surfaces of said seal means and arranged to permit relative longitudinal movement with respect to one another;   means actuated by a differential fluid pressure for biasing said first and second engaging means toward one another; and   means for substantially preventing contact of said seal means with the fluid in the environment of said housing.   
     
     
       2. The seal system of claim 1 wherein said means for preventing contact comprises a first fluid chamber positioned in the annular space between said shaft and housing above said first engaging means and having a fluid within said chamber and means for communicating the pressure of said fluid in said first chamber to said first engaging means. 
     
     
       3. The seal system of claim 2 further comprising means for communicating the pressure of the environment within the interior of said housing to said fluid in said first chamber. 
     
     
       4. The seal system of claim 2 further comprising a second chamber positioned in the annular space between said shaft and housing below said second engaging means and having a viscous material with said second chamber. 
     
     
       5. The seal system of claim 4 further comprising barrier means at the lower end of said second chamber for admitting pressure from the environment below said housing into said second chamber but at the same time preventing the entry of fluids from the environment below said housing into said second chamber. 
     
     
       6. The seal system of claim 1 wherein said biasing means comprises differential areas on the top and bottom surfaces of said one of said first and second engaging means to provide an unsupported area thereon for urging the engaging surface of at least one of said engaging means against the matingly engaging surface of said seal means. 
     
     
       7. The seal system of claim 6 further comprising spring means for constantly biasing the matingly engaging surface of said one of said engaging means against the matingly engaging surface of said seal means. 
     
     
       8. A rotary seal system for use in forming a seal between first and second members rotating relative to one another, comprising: annular slanted sealing means arranged in an annular slanted path between said first and second members and having substantially flat sealing surfaces engaging said first and second members;   upper and lower annular support members positioned above and below said sealing means, said annular support members each having annular slanted surfaces matingly engaging the annular slanted sealing means;   means actuated by a differential fluid pressure for urging at least one of said upper and lower annular support members toward the other; and   means for substantially preventing contact of said seal means with the fluid in the environment of said members.   
     
     
       9. The seal system of claim 8 further comprising a radius formed on the edges of at least one of said flat sealing surfaces. 
     
     
       10. The rotary seal system of claim 8 wherein said means for substantially preventing contact comprises a chamber containing a lubricating fluid within which said sealing means is positioned. 
     
     
       11. The rotary seal system of claim 10 wherein said seal means separates said chamber into a high pressure side and a low pressure side, and wherein a positive flow of lubricating fluid is maintained across said sealing means. 
     
     
       12. The rotary seal system of claim 8 wherein said seal means is in fluid communication on a high pressure side with a first chamber containing a lubricating fluid and is in fluid communication on a low pressure side with a second chamber containing a fluid having a viscosity greater than said lubricating fluid and wherein a positive flow of lubricating fluid is maintained across said sealing means. 
     
     
       13. The rotary seal system of claim 12 further comprising means for communicating the pressure of the environment within the interior of said members to said fluid in one of said chambers. 
     
     
       14. The rotary seal system of claim 12 further comprising means for communicating the pressure of the environment on the exterior of said members to said fluid in one of said chambers. 
     
     
       15. The rotary seal system of claim 12 further comprising barrier means between said fluids in said chambers and the fluid in the environment of said members, said barrier means capable of communicating pressure but substantially preventing communication of the fluid in the environment into said chambers. 
     
     
       16. In a borehole tool suitable for incorporation in a drill string in which a drilling fluid is pumped down the bore of the drill string and out the bottom of the drill string, said tool including a housing capable of incorporation on the lower end of the drill string, a rotating shaft carried within the housing, bearings positioned between the housing and the shaft for supporting the rotary movement of the shaft within the housing, the bearings being maintained within an oil bath, and a shaft rotation system connected to the shaft to cause the shaft to rotate within the housing when drilling fluid is pumped downwardly through the drill string, a sealing system for sealing the lower end of the housing and shaft to prevent drilling fluids from entering into the oil bath, a seal system comprising: annular seal means having an axially variable configuration about said rotating shaft so that one surface of said seal means slidably engages said rotating shaft;   first and second means engaging the top and bottom surfaces of said seal means and arranged for relative longitudinal movement with respect to one another;   means actuated by a differential fluid pressure urging said first and second engaging means toward one another; and   means for substantially preventing contact of said seal means with the fluid in the environment of said housing.   
     
     
       17. The seal system of claim 16 wherein said seal means is arranged in an oblique, slanted path about said rotating shaft. 
     
     
       18. The seal system of claim 16 wherein one of said first and second engaging means is an annular ring means vertically movable between said housing and shaft means and having a portion arranged to matingly engage one of said top and bottom surfaces of said seal means, said annular ring means having one of its top and bottom surfaces forming an unsupported area to urge it in the direction of the unsupported area, for biasing said portion of said annular ring means toward its mating engagement with one of said top and bottom surfaces of said seal means. 
     
     
       19. The seal system of claim 18 wherein said annular ring means has a surface thereon for matingly engaging the annular seal means. 
     
     
       20. The seal system of claim 18 further comprising an oil filled chamber adjacent said seal means, with said annular ring being positioned between said chamber and said seal means, and means for imparting the pressure of drilling fluid within the drill string to said oil filled chamber. 
     
     
       21. The seal system of claim 20 further comprising spring means in said chamber for imposing a longitudinal biasing force on said annular ring. 
     
     
       22. The seal system of claim 20 further comprising annular barrier means interposed between said housing and shaft and longitudinally spaced from the other of said top and bottom surfaces and the bottom of said housing and a viscous fluid in the longitudinal space between said annular barrier means and said other of said top and bottom surfaces. 
     
     
       23. The seal system of claim 16 further comprising first and second chambers adjacent said first and second engaging means respectively, with said engaging means positioned between said chambers and said annular seal with lubricating oil in one of said first and second chambers and a viscous medium in the other of said first and second chambers having a viscosity greater than that of said lubricating oil. 
     
     
       24. The seal system of claim 23 further comprising means for maintaining said chamber with lubricating oil at a higher pressure than said chamber containing a viscous medium. 
     
     
       25. The seal system of claim 16 wherein one of said first and second engaging means is an annular sleeve having a surface for matingly engaging the other of said top and bottom surfaces, and further comprising annular barrier means positioned between said housing and shaft and spaced from said annular sleeve to form a chamber between said annular sleeve and barrier means with a viscous material in said chamber.